Silver image transfer polymerization process



United States Patent Ofiice 3,345,164 SILVER IIVIAGE TRANSFER POLYMERIZATION PROCESS Abraham Bernard Cohen, Springfield, and Joseph Anthony Sincius, Little Silver, N.J., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Continuation of abandoned application Ser. No. 101,074, Apr. 6, 1961. This application Apr. 4, 1966, Ser. No. 539,665

12 Claims. (Cl. 96-28) This application is a continuation of Cohen and Sincius US. application Ser. No. 101,074 filed Apr. 6, 1961, now abandoned.

This invention pertains to photography and more particularly to a photographic process for the formation of photographic images. Still more particularly it pertains to processes for the transfer of photographic images from one layer into another.

In a conventional silver halide photographic process a latent silver image is produced by the direct action of light or other radiation on sensitized silver halide crystals dispersed in a suitable binder. Generally, this latent image is amplified through a chemical or physical development process in order to obtain a useful image. The efiiciency of a photographic system can be expressed by its quantum yield, i.e., the number of elementary reactions corresponding to one light quantum absorbed by the system. The photographic elementary process, i.e., the formation of the latent image, has a quantum yield of less than 1. The developing step increases this quantum yield to to 10 in other words, for each light quantum absorbed in the system 10 to 10 silver atoms are developed in the processed image.

Metal ions, including silver ions, have been widely used to catalyze peroxide initiated polymerizations. But all such processes operate in solutions for bulk polymerization, and no process is known which utilizes non-photolyzed silver halide in a photographic element to provide a selective, imagewise polymerization in solid phase.

In non-silver halide systems, the quantum yield is usually much lower because no amplification step occurs. Processes like those utilizing diazonium compounds or bichromated colloids provide a quantum yield of approximately 0.5. Exceptions are those processes in which the primary exposure initiates a chain reaction such as in an addition photopolymerization, where the photolytic activation of one monomer molecule can result in a polymer chain having many units of the original monomer. In these cases, the overall quantum yield is considerably higher than in other non-silver halide processes, but it is generally still far below the over-all quantum yield attainable in silver haliclephotography.

In practice, a difference in quantum yield usually manifests itself primarily in a difference in photographic sensitivity or speed. Other factors, like image structure and covering power, however, have an effect on the quantum yield-speed relationship.

For many applications of photography it is desirable to have still higher photographic speeds than those that are attainable with the present-day silver halide systems.

Such applications include, for example, high speed motion picture photography, low-dosage X-ray recording, available light and subdued light photography, oscillographic recording, astrophotography including photographing artificial satellites, etc. It is also desirable for many purposes to produce images of higher covering power than are attainable with silver images, as well as images varying in relief or in the degree of moisture sensitivity or permeability for photomechanical purposes. Although processes for the latter applications are known A 3,345,164 Patented Oct. 3, 1967 (tanning development of silver halide-colloid systems, dichromate or diazonium sensitized colloids, etc.) their over-all quantum yield is no higher and usually much lower than that of the corresponding parent photosensitive system.

It has been proposed to use silver nitrate or silver halide to initiate a photopolymerization reaction, imagewise (Phot. Sci. and Eng, 4, 151 (1960), and Belgian Patent 482,912), but the proposed processes are slow in comparison with silver halide processes or photopolymerization processes utilizing organic photoinitiators. It has also been claimed that the over-all quantum yield in silver halide photography can be increased by a factor of 10 by utilizing the semiquinone intermediates produced in photographic development to initiate polymerization (Nature, Dec. 7, 1959, p. 1275). In the examples given, however, the polymerization only serves to modify the state of aggregation and thus the covering power of the silver image, but no true increase in terms of amount of reduced silver, is achieved.

An object of this invention is to provide new and useful processes for the formation of photographic images. Another object is to provide simple and dependable processes for transferring photographic images to images of greater density. A further object is to provide such processes which do not require expensive or unique processing equipment. A still further object is to provide such processes which use commercially available materials. A still further object is to provide such processes which can be carried out in a short time by the ordinary technician. Still further objects will be apparent from the following description of the invention.

The silver salt image transfer-polymerization process of this invention comprises subjecting a silver salt image record while it is in image transfer relationship with a layer comprising a non-gaseous addition polymerizable ethylenically unsaturated compound containing at least one terminal ethylenic group, to the action of a peroxygen compound and a silver salt solvent or fixing agent that does not initiate addition polymerization until an image of addition polymer is formed in said layer. In general, the image in the form of the addition polymer ditfers in appearance or contrast, by reason of a change in optical density, from the non-image areas which still contain the addition polymerizable compound and material associated therewith, e.g., finely divided or dispersed filler material, addition polymerization initiator, inhibitor, etc. The contrast can be improved by the presence of a finely divided colorant, e.g., pigment or dye, in the polymerizable layer. After formation of the addition polymer image, addition polymerizable compound can be removed in the non-polymerized image areas. The silver salt solvent is generally applied as a transfer liquid; namely, as a dilute or viscous aqueous solution having a pH between 5 and 8.5, preferably between 6 and '8.

The silver salt image record can be the reverse image in an exposed and developed but unfixed colloid silver halide emulsion layer containing developed silver in the original image areas or can be the reverse image where the developed silver is removed by means of conventional photographic bleaching solutions to leave the unexposed and undeveloped silver salt image record. The original photographic element can be exposed to an original scene or printed from a negative or positive imagebearing transparency or stencil and can be a continuous tone, halftone or combination halftone and line image. The photographic silver halide emulsion layer can be on an opaque paper, film or other sheet support or on a transparent film base. In the case of the latter the exposure can be through the base.

Silver halide solvents or photographic fixing agents useful in accordance with the invention, in addition to dissolving silver halide, form mobile silver complex ions. The silver ions in the presence of a peroxygen compound catalyze or initiate addition polymerization of ethylenically unsaturated compounds. Among the useful silver halide solvents are sodium, potassium and ammonium thiosulfate and thiocyanate; sodium and potassium cyanide; ammonia, thiourea, thiosinamine; sodium chloride and potassium iodide. The silver halide solvent used should not induce addition polymerization.

In carrying out the invention, the silver salt image is usually present in a flexible film or paper element and the polymerizable layer is present in a separate sheet element, preferably one having a flexible film or paper sheet support. The silver salt image, however, may be present in the same element as that containing the polymerizable layer or stratum and suitable elements of this type are described in assignees Cohen US. application Ser. No. 86,598 filed Feb. 2, 1961, U.S. Patent 3,194,- 661July 13, 1965. In these latter elements, the silver salt image-bearing layer usually will be very thin and of the same order of magnitude as in a conventional photographic film having a gelatin-silver halide emulsion layer (i.e., about 0.1 to 10 mils in thickness).

In the case where the silver salt image is in a separate photographic silver halide emulsion layer, the latter will be in contact with a solid layer comprising the ethylenically unsaturated compound on a separate support, e.g., film, plate or paper. The two layers will be in surface contact during the image transfer addition polymerization reaction. After the polymer image is formed, the two layers are separated, thus removing the addition polymerizable compound from the silver salt image in the other layer but leaving it in the stratum of the separated layer containing the polymer image. In a subsequent treatment, the addition polymerizable compound in the non-polymer image areas can be removed by washing and/or dissolving it from said areas or it can be transferred by thermal transfer or solvent-transfer methods to a separate image-receptive support, for example, paper having a rough surface. Suitable thermal transfer methods and image producing procedures are described in assignees U.S. applications Ser. No. 850,522 filed Nov. 3, 1959, Patent 3,060,025ct. 23, 1962; Ser. No. 839,304 filed Sept. 11, 1959, Patent 3,060,024--Oct. 23, 1962; and Ser. No. 831,700 filed Aug. 5, 1959, Patent 3,060,023-Oct. 23, 1962.

The non-gaseous, addition polymerizable, terminally ethylenically unsaturated compound used in the solid stratum described above may contain 1-4 or more terminal ethylenic groups (CHFC have a boiling point above 80 C. at atmospheric pressure, and be capable of rapidly forming an insoluble high polymer by free radical-initiated, chain propagating, addition polymerization in the presence of an addition polymerization initiator therefor. The unsaturated compound, preferably a monomer, may be either liquid or solid but if liquid, a solid inorganic or organic filler material should be present in such an amount that the layer is solid. However, for applications where the monomers can be applied during processing, liquid compositions can be used. Suitable polymerizable strata and elements of this type for use in the image-transfer polymerization of the invention are described in U.S. Patents 2,760,863; 2,791,504; 2,892,- 716; 2,893,868; 2,902,365; 2,923,673; 2,927,022; 2,927,- 023; 2,929,710; 2,948,611 and 2,951,758.

When the final polymer image-bearing element is to be used in a thermal image transfer process, the solid stratum should be solid below 40 C. and thermally transferable by having a stick or transfer temperature above 40 C. and below 220 C. and comprise (a) a thermoplastic organic polymer solid at 50 C. and (b) an ethylenically unsaturated compound containing 1-4 terminal ethylenic (CH C groups having a boiling point above 100 C. at normal atmospheric pressure, being capable of rapidly forming a high polymer by free radical initiated addition polymerization, as stated above, and also having a plasticizing action on said thermoplastic polymer; said constituents (a) and (b) being present in amounts from 3 to 97 and 97 to 3 parts by weight resceptively. Any of the thermoplastic polymers and monomer combinations given in assignees Burg and Cohen U.S. application Ser. No. 831,700 filed Aug. 5, 1959, U.S. Patent 3,060,023, Oct. 23, 1962, can be used for the processes of this invention. For other methods of development the above restrictions necessary for thermoplastic character would not apply.

The silver salt image-polymerization transfer process of this invention, as disclosed above, can be carried out in a practical manner by applying to the surface of one of the two layers, i.e., the silver salt image-bearing layer or the polymerizable layer, an aqueous transfer solution. This solution will generally contain (1) water, (2) a silver halide solvent, (3) if necessary, a buffer to adjust the pH to the preferred range of 6 to 8, and (4) a thickening agent to increase the viscosity of the solution and to facilitate spreading of the solution uniformly over the entire transfer area. Solutions having a viscosity of 10 to 300 centipoises are useful. The thickening agents used in adjacent layers or contact development of exposed silver images to form developed silver images in separate silver halide layers are useful in the transfer solutions. Polyethylene oxide, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, glycerine, and ethylene glycol, diethylene glycol and their derivatives are useful thickening agents.

In carrying out the process of this invention, an enormous increase in quantum yield of the image is obtained. This increase is quite unexpected because the main amplification reaction which takes place in other processes takes place only in a solution system under ideal conditions, whereas the process of this invention embodies a solid, image-forming system. The process of this invention is designated as a silver halide-transfer polymerization process because a polymerization reaction is initiated by diffusion of silver ions into the sites of polymerization and while the theory of the reaction has not been fully established, the results might be explained (Where a thiosulfate is used as a silver halide solvent, persulfate as the peroxygen compound and an alkyl acrylate as the unsaturated monomer) by the following equations:

A similar sequence of reactions is believed to take place with other silver halide solvents and peroxygen compound-s.

The migration of silver ions from the silver salt sites to the ethylenically unsaturated monomer sites or polymerization sites produces free radicals which initiate the polymerization of the monomer (Equations 6 and 7). The over-all reaction, as far as starting material and end product are concerned, and the enormous quantum yield associated with the over-all reaction, are summarized in Equation 8. The cumulative quantum yield in accordance with the invention is quite surprising but it is even more surprising that the reactions (Equations 3--7) which involve rate determining diffusion steps can be completed in a matter of seconds at room temperature.

The invention will be further illustrated by but is not intended to be limited to the following examples. In these examples, where necessary, actinic light was excluded, and the percentages are by weight.

Example I A dilute, aqueous carbon black dispersion was prepared according to a process described in U.S. Patent 2,581,414 by rapidly stirring 52 grams of a mixture of a 40% aqueous dispersion of carbon black having an average particle size of 41 mu, 340 ml. of distilled water and 340 grams of 20 to 30-mesh Ottawa sand as referred to in A.S.T.M. specification C-190. After 5 minutes of stirring at room temperature in a stainless steel can of approximately 1500 ml. capacity, the sand was separated from the mixture by filtration through a layer of felt of about inch thickness.

A 40-ml. portion of the filtrate was added to 400 ml. of a solution containing 8% of photographic grade gelatin and 20% of methanol, kept at 30 to 40 C., and 15 ml. of a 5% aqueous solution of a surface active agent (the sodium salt of technical lauryl alcohol sulfate), were added to the gelatin-carbon dispersion.

A coating solution was prepared as follows:

Gelatin-carbon dispersion ml 100 Potassium persulfate solution, 1.33% ..ml 100 Polyethylene glycol diacrylate g 6.65

This coating solution was coated at about 35 C. on polyethylene terephthalate film made according to Alles et al. U.S. Patent 2,627,088 and Alles et al. U.S. Patent 2,779,684, consisting of a polyethylene terephthalate film having a coating of vinylidene chloride/ acrylic ester/itaconic acid copolymer and, over this coating, a thin (0.5 mg./dm. coating of gelatin.

A photographic film bearing a gelatino-silver halide photographic emulsion layer originally containing 70% AgCl and 30% AgBr was exposed through an imagebearing negative bearing both line and halftone images. The exposed photographic film was then developed in a standard aqueous lithographic developing solution containing N-methyl-p-aminophenol and hydroquinone as developing agents, washed in water and dried without fixing. The photographic emulsion layer bearing a developed positive silver image and a reverse silver salt image was treated with 0.1-molar sodium thiosulfate in a 2% by weight aqueous solution of a polyethylene oxide having a molecular weight of about 100,000 and a viscosity such that a 5% by weight aqueous solution had a viscosity of 225-375 centipoises at 25 C. The so-treated emulsion layer was then brought into intimate, uniform contact with the gelatin carbon black addition-polymerizable layer of the previously described transfer film by passing the two films while in surface contact between rubber rollers under a slight pressure and then placed in a vacuum frame for about one minute to insure that intimate contact between the two layers was maintained.

Upon separation of the two layers, the unpolymerized areas, corresponding to the silver image in the lightsensitive layer, were removed by washing for 3 minutes in an agitated water bath kept at 40 C. The resulting pigmented polymer image was a positive copy of the original silver image, i.e., the black areas of the polymer image corresponded to the black areas of the photographic image.

Example 11 Example I was repeated except that the transfer solution instead of being 0.1-molar sodium thiosulfate was l-molar sodium chloride in the 2% by weight aqueous polyethylene oxide. Similar results were obtained.

In the foregoing examples, the polyethylene glycol diacrylate referred to was the diacrylic acid ester of a mixture of polyethylene glycols where the latter precursor had an average molecular weight of 300.

The polymerization in the silver halide (non-image) areas, but not in the silver (image) areas is accomplished by the use of a nearly neutral transfer fluid. Under these conditions the oxidation of the metallic silver ions proceeds only slowly whereas the solvent action of the thiosulfate on the silver halide is rapid. Thus, the silver ion concentration necessary to catalyze the polymerization reaction is reached much faster in the silver halide areas than in the silver areas. The polymerization reaction in the silver halide areas is completed before the necessary silver ion concentration in the silver areas is reached to produce a significant amount of polymer.

Example Ill Example II was repeated, except that the pigmented layer did not contain any potassium persulfate. The transfer solution, besides containing polyethylene oxide and sodium chloride as in Example H, was 0.1 molar in potassium persulfate. The results were similar to those of the previous examples.

Example I V Example III was repeated except that the polyethylene glycol diacrylate monomer in the pigmented layer was replaced by the same amount of acrylamide. The results were similar to those of the previous examples.

Example V The following coating solution was prepared: 8% gelatin in 20% aqueous methanol ml 5% aqueous sodium dodecyl sulfate ml 4 Polyethylene glycol diacrylate g 6.65 o-Mcthacrylarnidophenol (20% in ethanol) ml 5 This solution was coated on polyethylene terephthalate film as described in Example I. A developed, but not fixed, continuous tone photographic negative was used in carrying out a silver halide transfer-polymerization reaction according to Example III, using a transfer liquid consisting of a solution l-molar in sodium chloride, 0.1-molar in potassium persulfate and containing 2% by weight of polyethylene oxide.

After separation of the two layers, the transfer layer was washed for 3 minutes in a solution of 3 parts of ethanol and 1 part of water to remove the unpolyrnerized o-lmethacrylamidophenol. The polymerized, colorless, im-

age was then developed with an alkaline solution of p-aminodiethylaniline containing potassium ferricyanide. A continuous tone, cyan colored, positive image of the original silver negative was obtained.

Example VI prepared by stirring lauryl alcohol sulfate. From this mixture the following coating composition was formulated:

Pigment/ gelatin blend g 10 aqueous lauryl alcohol sulfate (Na salt) ml 4 6% polyethylene oxide (see Example I) ml 20 Polyethylene glycol diacryate g 2 Potassium persulfate g 0.2

This mixture was coated on polyethylene terephthalate film base, described in Example I, at 35 C. and dried. A silver halide transfer polymerization was then performed as described in Example I with a developed and washed, but unfixed photographic positive. On separating the pigmented coating and the silver positive, the polymer image remained attached to the silver halide areas and was completely stripped from the gelatin/ pigment coating. Thus, a wrong reading, pigmented positive image remained, Whereas the silver halide areas of the original silver positive were overlaid with a contiguous, pigmented image. After bleaching of the silver image with a photographic bleaching solution, a right reading, pigmented negative image remained on the film.

Example VII Cellulose acetate butyrate g 90 Polyethylene glycol diacrylate g 27 Carbon black dispersion ml 170 Acetone ml 1312 This mixture was coated on polyethylene terephthalate film to give a dry coating thickness of 0.0002 inch. A photographically developed and washed, but unfixed positive line image containing developed silver image areas and undeveloped silver halide image areas was lightly brushed with a transfer solution consisting of an aqueous solution containing 2% of polyethylene oxide, 2% of hydrogen peroxide, being 2-molar in sodium chloride and having a pH of 7.0. The so treated photographic element was brought in intimate contact with the above described coating for 10 seconds by placing the sandwich in a vacuum frame. On separation of the two sheets, the areas that were in contact with the silver halide areas were found to be polymerized. The pigmented layer was then covered with a white bond paper and the assembly passed between rollers heated to 120 C. and exerting a total force of 5 lbs. The unpolymerized areas were found to be transferred to the bond paper, giving a pigmented image which was a duplicate of the original silver image.

In the foregoing examples, the polyethylene diacrylate used was a mixture of diacrylates of polyethylene glycols containing an average of 8 ether groups.

The characteristics of the polymer image obtained by this new image forming process can be varied over a Wide range by properly selecting the various components of the image forming element. Thus, if maximum contrast is required the pigment used should be dark, preferentially black. A carbon black dispersion is the preferred pigment, but other materials, such as organic and inorganic pigments that are not decomposed or changed by the oxidizing agents used, can be substituted. Pigments of another color than black lead to correspondingly colored polymer images. For some applications, a pigment-free polymer image is suflicient, for example, for offset printing plates where the printing surface is differentiated by hydrophobic and hydrophilic areas. The color and type of pigment have no influence on the process involved so long as no chemical reaction involving the pigment occurs. In general, the pigment will be present in an amount of 2 to 50% based on the total weight of the polymerizable layer.

The optical density of the polymer image is independent of the silver halide density of the photographic image; it is determined by the amount and type of pigment or dye added to the polymerizable layer and by the layer thickness. Thus, amounts of silver halide which would give low density images, if developed conventionally, can give intense images by catalyzing the decomposition of a peroxygen compound to produce a highly pigmented polymerized image.

A suitable binder for the polymerizable layer is gelatin, but for some applications other binders are advantageous. The binder used should be permeable to the solvent used for the solution of the peroxygen compound. Thus, in the preferred system, water-permeable binders such as polyvinyl alcohol, polyacrylamide, polyvinyl pyrrolidone, cellulose acetate succinate, polyethylene oxides, bone glue, agar-agar, methyl cellulose, or copolymers of hydrophobic vinyl monomers with hydrophilic monomers such as acrylic acid, acrylamide, sodium styrene sulfonate, etc. or certain nylons that are soluble in aqueous systems, for example the alkoxymethyl nylons and the compounds disclosed in Burg, US. application S.N. 753,196, filed Aug. 5, 1958, Patent 3,043,805, July 10, 1962, can be used. Where water-insoluble peroxides are used such as benzoyl peroxide in ethanol, the process operates best with binders which are alcohol-permeable such as cellulose acetate or cellulose acetate butyrate, polyvinyl acetate, polyvinyl butyral, ethyl cellulose, certain nylons, etc. The selection of the binder depends to some degree on the method of development. Thus, if the image is to be developed by water washout, the binder should be soluble in water or for alcohol washout, in alcohol. Where development is by thermal transfer, a preferred binder monomer combination should have a reasonably low softening point. It is even possible to use no binder at all, by selecting a monomer which in itself is film forming.

The polymerization reaction of this invention depends on making available an imagewise distributed silver ion catalyst from the silver halide areas of a light exposed and developed element either in the presence or absence of the silver image areas. These silver ions are formed in situ by reacting a silver halide solvent with unexposed silver halide while suppressing oxidation of the silver image areas which could also yield silver ion. Any type of light sensitive silver salt system can be used to produce the original silver image, for example, ordinary photographic emulsions containing silver chloride, silver bromide, silver iodide or mixtures thereof or structures containing other light sensitive silver salts, like silver oxalate, silver acetylide, silver azide, etc. They can be sensitive to various radiations, like visible light, ultraviolet or infrared radiation, X-rays, alpha-, beta, or gamma-radiation, etc., or to mechanical deformations like pressure.

Any polymerizable vinyl compound that is soluble or dispersible in water or in a solvent, for example in ethanol, methanol, acetone, etc., can be used in practicing the invention. Suitable vinyl compounds which can be used in place of those described in the examples include acrylic acid, methacrylic acid, acrylamide, methacrylamide, methyl acrylate, ethyl acrylate, methyl methacrylate, vinyl acetate, methyl vinyl ketone, 2-methyl-5-vinyl pyridine, styrene, etc. Also, alkylene or polyalkylene glycol diacrylates prepared from alkylene glycols of 2 to 15 carbon atoms or polyalkylene glycols of 1 to 10 ether linkages, and the additional polymerizable monomers disclosed in Martin & Barney, US. Patent 2,927,022, Mar. 1, 1960, having a plurality of addition polymerizable ethylenic linkages, and especially those wherein at least one and preferably most of the terminal ethylenic linkages are conjugated with a doubly bonded carbon, including carbon doubly bonded to carbon and to such heteroatoms as nitrogen, oxygen and sulfur. Outstanding are such materials wherein the ethylenically unsaturated groups, especially the vinylidene groups, are conjugated with ester or amide structures. The following specific compounds are further illustrative of this class:

Unsaturated esters of polyols, particularly such esters of the alpha-methylene carboxylic acids, e.g., ethylene diacrylate, diethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate, ethylene dimethacrylate, 1,3- propanediol dimethacrylate, 1,2,4butanetriol trimethacrylate, 1,4-cyclohexanediol diaorylate, 1,4-benzenediol dimethacrylate, pentaerythritol tetramethacrylate, 1,3- propanediol diacrylate, 1,5-pentanediol dimethacrylate, the bisacrylates and methacrylates of polyethylene glycols of molecular weight 200-500, and the like; unsaturated amides, particularly those of the alpha-methylene carboxylie acids, and especially those of alpha,omegadiamines and oxygen-interrupted omega-diamines, such as methylene bis-acrylamide, methylene bis-methacrylamide, ethylene bis-methacrylamide, 1,6-hexamethylene bis-acrylamide, diethylene triamine tris-methacrylamide, bis(gamma-methacryl-amidopropoxy)ethane, beta-methacrylamidoethyl methacrylate, N- (beta-hydroxyethyl)- beta(methacrylamido)ethyl acrylate and N,N-bis(betamethacrylyloxyethyl)acrylamide; vinyl esters such as divinyl succinate, divinyl adipate, divinyl phthalate, divinyl terephthalate, divinyl benzene-1,3-di-sulfonate, and divinyl butane-1,4-disulfonate; acrylate salts, such as calcium acrylate, magnesium acrylate, etc.; and unsaturated aldehydes, such as sorbaldehyde (hexadienal).

The polymerization initiator is a peroxygen compound. Potassium persulfate is the preferred initiator, but other peroxygen compounds are useful, for example, sodium and ammonium persulfat-e, hydrogen peroxide, benzoyl peroxide, succinic acid peroxide, t-butyl hydroperoxide, sodium perborate, and others.

The polymerization reaction is initiated by contacting the polymerizable layer with a silver halide image layer in the presence of a peroxygen compound and a silver halide solvent. While both ingredients must be present it is not necessary that they be added together, e.g., the peroxygen compound may already be present in the polymerizable element and only the silver halide solvent is added during processing. For imagewise polymerization, it is essential that the silver halide solvent and processing conditions be selected so that the silver halide solvent and peroxygen compound do not interact to initiate overall, non-selective polymerization. Also, if both silver and silver halide are present, it is necessary to suppress the oxidation of silver by the peroxygen compound. It has been found that this can be done by control of pH, since the oxidation of silver by the peroxygen compound is only rapid at low pH conditions.

While this selective polymerization by silver halide is operative in the presence of silver image areas, it may be desirable in some instances to oxidize the silver image first by any of the usual photographic bleaching processes prior to the polymerization process. In such cases it is not necessary that the pH of the solution containing the peroxygen compound be above the range where it would attack the silver, since the only available silver ion would be from solubilization of the silver halide.

The peroxygen compound and silver salt solvent can be added to the transfer fluid used to promote contact between the image and the polymerizable layer. This eliminates any premature decomposition of the highly reactive peroxygen compound and therefore increases the shelf life of the polymerizable layer.

The transfer time can vary considerably. Since lateral diffusion can occur and reduce resolution, the time should 'be kept as short as possible.

Sharpness can also be increased by the use of thin layers which minimize lateral diffusion. Since the covering power of the pigmented layers is very high and since the amount of silver required in the light sensitive layer is low, this system lends itself readily to thin layers.

In those applications where a silver halide layer and a polymerizable layer are coated one over the other on the same support or where a suit-able vinyl monomer is added to a liquid silver halide emulsion and the mixture coated on a support the use of a transfer fluid is not required. However, it is preferred not to incorporate the peroxygen initiator into the coatings, but rather to treat the exposed, composite coating with a solution of the initiator and the silver halide solvent.

The peroxygen compound concentration in the transfer fluid is generally adjusted from 0.01-molar to 2-molar, preferably from 0.05-molar to 0.2-molar. A higher initiator concentration requires a shorter contact time of the two layers. With some peroxygen compounds the concentration is limited by their solubility.

If the peroxygen compound is incorporated in the gelatin/monomer coating, an amount of 1 to 30% based on the monomer weight is satisfactory. Usually, 10 to 20% were used, the higher amounts giving more rapid polymerization.

The utility of the processes and products of this inven- *tion have been described in the foregoing text and especially in the examples. The invention, however, is not limited to merely increasing the quantum image yield of silver halide photographic images but as will be apparent to those skilled in the photographic and related arts, is useful for many practical purposes. For example, the process of the invention can be used in the preparation of lithographic printing plates which are characterized by exceedingly shallow reliefs and by having ink-receptive and ink-repellent areas. By having both hydrophobic materials and hydrophilic materials in respective areas lithoplates can be made. The invention is useful in preparing halftone and line letterpress printing plates as well. Plate production is greatly simplified by the invention. In addi tion, greater speeds are possible because no photographic exposure of the polymerizable plate is necessary.

The process of the invention can be used to prepare resist images for screen printing, for etching, for the preparation of printed circuits, etc.

Another advantage of the invention is that satisfactory high-contrast off-set plates can be prepared from lowcontrast silver halide photographic materials and without the intermediate photographic steps often used to increase contrast. Still other advantages will be apparent from the foregoing description of the invention.

We claim:

1. A photographic image transfer-polymerization process which comprises subjecting a photographic silver halide continuous tone, halftone or line image record of a silver halide emulsion layer wherein any metal-containing image-yielding material in association with said layer is a silver containing material to the action of (1) an aqueous solution having a pH between 5 and 8.5 of a silver halide solvent selected from the group consisting of sodium, potassium and ammonium thiosulfate and thiocyanate; sodium and potassium cyanide; ammonia, thiourea, thiosinamine, sodium chloride and potassium iodide that does not initiate (2) a peroxygen compound, while said record is in contiguous image transfer relationship with a stratum comprising at least one non-gaseous, addition polymerizable, ethylenically unsaturated compound containing at least one terminal ethylenic group, and maintaining the stratum in such relationship while diffusing the silver ions formed from the silver halide solvent and the silver halide record from the silver halide sites to the sites of the monomer or of polymerization -until an image of addition polymer corresponding to the silver halide image is formed in said stratum.

2. A process according to claim 1 wherein said stratum is a solid stratum.

3. A process according to claim 1 wherein the silver halide image record is in the same layer as the ethylenically unsaturated compound.

4. A process according to claim 1 wherein the silver halide image record is in a separate layer from the ethylenically unsaturated compound.

5. A process according to claim 1 wherein the silver halide image record is in an outer layer on one support and the ethylenically unsaturated compound is in an outer layer on a separate support.

6. A process according to claim 1 wherein said silver halide solvent is sodium thiosulfate.

7. A process according to claim 1 wherein the silver halide image record is in a thin gelatin layer.

8. A process according to claim 1 wherein said stratum contains a colorant.

9. A process according to claim 1 wherein said aqueous solution is a viscous solution.

10. A process according to claim 1 wherein said stratum contains an organic polymer solid at 50 C. and the ethylenically unsaturated compound contains 14 terminal ethylenic groups, has a boiling point above 80 C. at

normal atmospheric pressure and is capable of rapidly forming a high polymer by free radical initiated, chainpropagating addition polymerization, and said polymer and ethylenically unsaturated compound are present in amounts from 3 to 97 and 97 to 3 parts by weight, respectively.

11. A process according to claim 1 wherein, after the image of addition polymer is formed, remaining addition polymerizable compound is removed by means of a solvent therefor.

12. A process according to claim 1 wherein the unpolymerized areas remaining in the said stratum after the image of addition polymer is formed are transferred to a separate support.

No references cited.

NORMAN G. TORCHIN, Primary Examiner.

J. H. RAUBITSCHEK, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,345 ,164 October 3 1967 Abraham Bernard Cohen et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 10, line 59, after "initiate" insert addition polymerization, and

Signed and sealed this 22nd day of October 1968.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PHOTOGRAPHIC IMAGE TRANSFER-POLYMERIZATION PROCESS WHICH COMPRISES SUBJECTING A PHOTOGRAPHIC SILVER HALIDE CONTINUOUS TONE, HALFTONE OR LINE IMAGE RECORD OF A SILVER HALIDE EMULSIONLAYER WHREIN ANY METAL-CONTAINING IMAGE-YIELDING MATEIAL IN ASSOCIATION WITH SAID LAYER IS A SILVER CONTAINING MATERIAL TO THE ACTION OF (1) AN AQUEOUS SOLUTION HAVING A PH BETWEEN 5 AND 8.5 OF A SILVER HALIDE SOLVENT SELECTED FROM THE GROUP CONSISTING OF SODIUM, POTASSIUM AND AMMONIUM THIOSULFATE AND THIOCYANATE; SODIUM AND POTASSIUM CYANIDE; AMMONIA, THIOUREA, THIOSINAMINE, SODIUM CHLORIDE AND POTASSIUM IODIDE THAT DOES NOT INITIATE (2) A PEROXYGEN COMPOUND, WHILE SAID RECORD IS IN CONTIGUOUS IMAGE TRANSFER RELATIONSHIP WITH A STRATUM COMPRISING AT LEAST ONE NON-GASEOUS, ADDITION POLYMERIZABLE ETHYLENICALLY UNSATURATED COMPOUND CONTAINING AT LEAST ONE TERMINAL EHTYLENIC GROUP, AND MAINTAINING THE STRATUM IN SUCH RELATIONSHIP WHILE DIFFUSING THE SILVER IONS FORMED FROM THE SILVER HALIDE SOLVENT AND THE SILVER HALIDE RECORD FROM THE SILVER HALIDE SITES TO THE SITES OF THE MONOMER OR OF POLYMERIZATION UNTIL AN IMAGE OF ADDITIN POLYMER CORRESPONDING TO THE SILVER HALIDE IMAGE IS FORMED IN SAID STRATUM. 